The technology disclosed in the present specification relates to a video format determination device and a video format determination method that are used to determine the format of a video signal, and a video display device that switches display modes of a video signal based on a format determination result, and more particularly, to a video format determination device, a video format determination method, and a video display device that realize reliable determination of a three-dimensional video format or two-dimensional video format with a small calculation amount.
A viewer can be presented with a stereoscopic video that can be three-dimensionally seen by displaying a video using parallax between right and left eyes. For example, a time-division stereoscopic video display system includes a combination of a display device that displays a plurality of different videos in a time-division manner and eyeglasses that video viewers wear. The display device alternately displays left-eye images and right-eye images having parallax at very short time intervals. In addition, while a left-eye video is displayed, the left eye part of the eyeglasses transmits light, and the right eye part thereof is shielded from light. On the other hand, while a right-eye video is displayed, the right eye part of the eyeglasses transmits light, and the left eye part is shielded from light. In addition, in a space-division stereoscopic video display system, a left-eye video and a right-eye video are multiplexed and displayed on one screen, and the left eye part of eyeglasses that a viewer wears only transmits light of the left-eye video, and the right eye part thereof only transmits light of the right-eye video. In both systems, the brain of a user who views the video fuses the left-eye video and the right-eye video so as to recognize the fusion as a stereoscopic video.
As transmission formats of three-dimensional video signals, for example, three types of a side-by-side format, a top-and-bottom format, and a frame sequential format can be exemplified. In the side-by-side format, active regions of two-dimensional video signals are divided into two halves in the horizontal direction as shown in FIG. 23, and a (concurrent) left-eye video L and a right-eye video R are multiplexed to the left and right sides, that is, in the horizontal direction. In addition, in the top-and-bottom format, active regions of two-dimensional video signals are divided into two halves in the vertical direction as shown in FIG. 24, and a (concurrent) left-eye video L and right-eye video R are multiplexed to the upper and lower sides, that is, in the vertical direction. In the frame sequential format, left-eye videos L and right-eye videos R are alternately inserted on a time axis as shown in FIG. 25.
Any of the transmission formats controls a display device that processes video signals such that left-eye videos and right-eye videos are separated from the signals, correctly arranged on the time axis, and thereby the left-eye videos are displayed for the left eye and the right-eye videos are displayed for the right eye. In this case, it is of course necessary to switch a display format by determining whether or not the video signal currently transmitted is for three-dimensional videos, and if the signal is for three-dimensional videos, determining in what transmission format shown in any of FIGS. 23 to 25 described above the signal is.
If a signal indicating a transmission format is added to transmitted video data, the determination can be accurately made. However, there are some broadcasting signals and DVDs (Digital Versatile Discs) to which such a signal is not added. In addition, there is content of which signals have different transmission formats, such as two-dimensional video content of a TV commercial, and three-dimensional video content of a TV program. Manually switching display modes every time signals are switched is very inconvenient for a viewer. If a display mode for which a video format is wrong is selected, an inconvenient incident in which two different types of images are displayed overlappingly occurs.
There are several proposals for devices that determine a video format from correlation of regions respectively corresponding to a left-eye video and a right-eye video in an image. For example, a proposal for a video display device that switches a display format by obtaining a position histogram from difference values in units of pixels to calculate correlation, and determining whether or not the result is for three-dimensional video has been made (for example, refer to Japanese Unexamined Patent Application Publication No. 2010-68309). In addition, another proposal for a stereoscopic image format determination device that automatically determines a format from the inner product of feature amounts of each region of a left-eye video and a right-eye video has been made (refer to Japanese Unexamined Patent Application Publication No. 2006-332985).
In the method for determining a format having the correlation between respective left- and right-eye video regions in a video signal as an index, determination of whether data is for three-dimensional video or two-dimensional video is made by obtaining predetermined feature amounts from the video regions and having a cumulative result of the absolute difference value between the feature amounts as estimation values. Herein, when an evaluation value is small, the correlation between the left- and right-eye video regions is high, and thus it can be determined that the respective regions are in the relationship of corresponding left and right videos, in other words, data is for three-dimensional video. Conversely, when an evaluation value is large, the correlation between the left- and right-eye video regions is low, and thus it can be determined that the respective regions are not in the relationship of corresponding left and right videos, and the data is for two-dimensional video.
However, if evaluation is performed merely based on the calculation of the correlation between left- and right-eye video regions, there are problems in terms of performance in that determination accuracy is low, and reliability is hard to guarantee.
For example, since there is parallax between a left video and a right video in a stereoscopic video, the correlation between the videos is low when the parallax is large, and thus there is a possibility of making erroneous determination that the video is not a three-dimensional video. FIG. 26 shows a result of an absolute difference value ABS (Lch-Rch) of feature amounts by simply matching the feature amounts of a left-eye video (Lch) and a right-eye video (Rch) having parallax. As shown in the drawing, when parallax is large, a difference is generated between videos, accordingly the correlation is low, and as a result, there is a possibility of making erroneous determination that the video is a two-dimensional video.
In addition, there is a possibility of making erroneous determination that a video is not a three-dimensional video due to a difference other than parallax between left and right videos. There is no problem in a CG (Computer Graphics) video, or the like, but particularly in the case of a three-dimensional video photographed using a twin lens camera, luminance, contrast, 7, color, bands of video signals, a noise amount, and the like may be significantly different between left and right videos due to differences in characteristics, differences in installation accuracy of lens systems, and the like. FIG. 27 shows a result of an absolute difference value ABS (Lch-Rch) of a feature amount by simply matching the feature amounts of a left-eye video (Lch) and a right-eye video (Rch) showing differences in luminance and contrast. As shown in the drawing, the difference is further made between videos when the differences in luminance and contrast are great, the correlation thereof becomes low, and thus a possibility of making erroneous determination that the videos are two-dimensional videos continuously increases.
Conversely, there are also cases in which a two-dimensional video is erroneously determined to be a three-dimensional video if videos having a high correlation between regions respectively corresponding to a left-eye video and a right-eye video are included therein. FIG. 28 shows an image of a seascape as an example of an image showing an insufficient change in luminance and contrast, and since the difference in the feature amounts on the left and right sides of the image is small and a high correlation is shown, there is a possibility of the image being erroneously determined as a three-dimensional video in the side-by-side format.
In addition, during determination of a video format, the evaluation method merely using calculation of the correlation between left- and right-eye video regions includes calculation in units of pixels and calculation of an inner product, which causes a large calculation amount, and therefore the amount adversely affects fast determination and costs.